This invention relates generally to the field of distributed RF (Radio Frequency) amplifiers. More particularly, this invention relates to stabilization of distributed amplifiers under high VSWR (Voltage Standing Wave Ratio) conditions.
Load variations that often appear at the intended output terminals of a distributed amplifier can result in a reverse standing wave across the amplifier""s distributed output network. This can place low or high impedance nulls at one or more of the distributed device drain or collector terminals causing instability or oscillation. Conventional linear distributed amplifier circuits are often implemented with a reverse wave resistive output termination in parallel with the intended output load. Use of a reverse wave termination resistor (i.e., a dummy load resistor), reduces the magnitude of the null impedance conditions eliminating generation of undesired non-harmonically related signals. Unfortunately, the penalty for using this reverse wave termination resistance is a reduction in output power level which also reduces the DC to RF conversion efficiency of the distributed amplifier. When such circuits are used in a battery powered transceiver product, reduced RF power amplifier conversion efficiency translates to a reduction in battery life.